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Cam Change

  
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Cam Change

 
bradshdj bradshdj
New User | Posts: 45 | Joined: 02/13
Posted: 01/11/14
02:28 AM

You guys havent steered me wrong yet so I have to ask another question.  I am like a nuicance fly.

I recently put a Comp Cam 268H in my 74 TA.  I really noticed a difference but now as you probably predicted its not 100% what I was looking for.

I have decided on one of two Cams to replace it later.  Both Comp Cams.  XE268 or XE274.  The 268H uses Comp Cam Springs 988 and the XE268 and XE274 uses 995 Springs.  What are the cons of leaving the 988 springs in the heads instead of changing em to 995 springs?  The Comp Cam Recommendations says Machining of heads required.  I am assuming that the milling is for the larger and stiffer springs.  What does this machining consist of.

Thanks for your great tips

Danny  

shyrgfuh3 shyrgfuh3
Enthusiast | Posts: 496 | Joined: 11/13
Posted: 01/11/14
02:55 AM

Hello bradshdj;


70 bird here, some of us lost our screen names with a site modification.

You are a pleasant nuisance.

Are you back in the states again?

I forgot, did you already have that cam or was it suggested to you?

Are you set on the xe274h?

You should have at least 9.5:1 static compression with the 274 cam and at least 331  gears with a stall conv if it is a 400 ci engine in my experience.
If you have stock heads it will benefit from a port job on them.

I as well as possibly a few others here are EXTREMELY familiar with that cam.

Comp has a zillion springs, we need to know exactly what your trapped spring height is before we can best help you..  

bradshdj bradshdj
New User | Posts: 45 | Joined: 02/13
Posted: 01/11/14
08:11 AM

No, I am back overseast but I get home in about four days.  The car is going to get its final work done to the interior this time home and she will be very nice.  Gonna post some more photos of her.  If I need 9.5-1 for the 274 then I will go for the XE268.  

When Comp Cam recommends milling the heads, is that for the springs so they stay in place on the floor of the head?  

I was looking at tensions on the springs and the max tension on the 988 springs which are in the head now is approximately 230 lbs according to the comp cam chart.  I believe it was in the high 300s in the 995s.  

I already had that 268H cam and I must admit the engine is well mannered and idles well with a noticeable lope.  Nothing radical but I have noticed in the higher RPMs it seems to be lacking a little.  That is why I was hoping for a cam with a bit more power in the higher RPMs.  

But I am satisfied with the overall performance of the car with the 268H cam, but for some reason, I guess we are never satisfied with the power.\

On another issue, anyone on here had any dealings with Kauffman Racing or Tin Indian Performance?  

idrivejunk idrivejunk
Addict | Posts: 5172 | Joined: 12/09
Posted: 01/11/14
08:20 AM

I believe its the spring pocket that needs work, like you suspected. Due to outer spring diameter. Those 995s are triple springs. I have a set of 4X-4H heads in my garage with those 995 springs installed if you need to inspect via photo. I ended up with the high dollar retainers and locks probably due to the valves selected. Been a long time and I don't know much about heads but I do have the 995 springs mounted on some, and if it will help you I can unwrap one and get a pic or two. But thats about it. I put the heads on a tired 400 with a lopey mystery cam, and almost instantly destroyed the engine by wiping the cam flat. The machinist saw me coming.  
idrivejunk

bradshdj bradshdj
New User | Posts: 45 | Joined: 02/13
Posted: 01/11/14
08:23 AM

No, I am back overseas but will be home in a few days

I picked out the 268H, and it runs good, but seems to be a little light on power in the higher RPMs.  I was hoping for a bit more top end power.

I am not set on any cam.  If the XE274 needs higher compression I will steer towards the XE268.

When comp cams recommendations states machining recommended, what does that mean for the 995 Springs?

Some pics of my 74 TA are in the Readers Rides.  Its the White TA.  She is running good, I am happy with it overall.  I just want a bit better power in the higher RPMs

Danny  

shyrgfuh3 shyrgfuh3
Enthusiast | Posts: 496 | Joined: 11/13
Posted: 01/11/14
08:29 AM

oops double vision  

shyrgfuh3 shyrgfuh3
Enthusiast | Posts: 496 | Joined: 11/13
Posted: 01/11/14
08:29 AM

Hi;



COMPRESSION - This is a lengthy subject. You do not "need" 9.5 for the 274 but all cams work best when the "optimal" amount of compression is used.

In other words, you "can", put a 288 cam in an engine with only 7.5 compression, and it will, still "run", but it will be a huge pig, because there is not enough compression. Ok, that's my technical description for the day.



MAX RPM - In my experience, you will hit around 5500 with an xe274h, at which point it will simply stop building rpm. The comp xe series cams have very little "over run", but its not really a problem.

What is your current max RPM?



MILLING SPRING PAD- It's typically done because the id of the spring is too large. Forget what they say for now and simply tell us what your exact trapped spring height is.


Don't forget, if your heads are stock and unported the 274 is a bad choice imo.  

bradshdj bradshdj
New User | Posts: 45 | Joined: 02/13
Posted: 01/11/14
08:31 AM

I did the same on a set of 6X heads years back with a way too radical cam and didnt change the springs.  This is why I am asking with only a step up from .454 lift to .470 lift.  Of these two cams the Intake duration is the same but the exhaust only increases from 218 degrees to 224 degrees.  Its not a huge jump in a cam but I dont want to harm the engine by saving a couple of bucks.  I would rather spend it now if I have to than later.  

bradshdj bradshdj
New User | Posts: 45 | Joined: 02/13
Posted: 01/11/14
08:35 AM

Well since we are having the conversation, I have a set of #16 D Port heads from a 68 428.  Will my compression be to high if I run it on my TA with 93 octane pump gas?  

bradshdj bradshdj
New User | Posts: 45 | Joined: 02/13
Posted: 01/11/14
08:36 AM

Sorry, its a WT block 400 ci from 74  

shyrgfuh3 shyrgfuh3
Enthusiast | Posts: 496 | Joined: 11/13
Posted: 01/11/14
08:40 AM

What is your current closed and open spring pressure?

We can't guess at spring rate for you.  

shyrgfuh3 shyrgfuh3
Enthusiast | Posts: 496 | Joined: 11/13
Posted: 01/11/14
08:49 AM

Icon Quotebradshdj:
Well since we are having the conversation, I have a set of #16 D Port heads from a 68 428.  Will my compression be to high if I run it on my TA with 93 octane pump gas?



You will need to cc them.

If your block has NOT been surfaced and your bore is .030" over you get the following:

72 cc = 9.95 comp, may or may not need higher octane than 93. E15 corn gas might work. E85 will work for sure.

Use a .060" thick head gasket = 9.55, 93 octane, nice!

75 cc = 9.67, 93 octane, hoorah!


PORTING - I would NOT install them unless I at least had them pocket ported and had the intake valves back cut.

You need screw in studs.